Chapter 7: Sedimentary Rocks

Question 1

What are sediments?

Answer 1

Any solid that settles to the bottom of a liquid

Question 2

What are detrital sediments?

Answer 2

Particles derived from weathering of pre-existing rocks

Transported a distance from its source

Question 3

What are chemical sediments?

Answer 3

Precipitate or are extracted by organisms

Forms where is deposits

Question 4

What are sedimentary rocks?

Answer 4

Composed of sediments

Make 5% of the crust

Host for many resources
(Oil, gas) banded formations

Question 5

What is the procedure to make sedimentary rocks

Answer 5

Weathering, erosion, sediment transportation

Question 6

What are the particle sizes?

Answer 6

Biggest to smallest:

Gravel
Sand
Silt 
Clay
Mud

Question 7

What is sorting?

Answer 7

Size distribution of particles

Poor: particles of different sizes

Well: particles same size

Question 8

How does sediment become sedimentary rocks?

Answer 8

Through lithification

Compaction: volume of sediments decrease weight of overlying sediment causes a reduction in pore space as particles pack more closely together

Cementation: glues the sediments together.
The most common cements:
Calcium carbonate and silica

Calcium carbonate readily dissolved in water with carbonate acid. Chemical weather of felspar yield silica solution

Question 9

Names the detrital sedimentary rocks.

Answer 9

Classic texture

1. Conglomerate- gravel sized particles, rounded
2. Breccia- gravel sized particles, angular
3. Sandstone- sand sized particles, classified based on mineral content
4. Mudrock- silt and Clay - sized particles
   i siltstone: silt
   ii mudstone: mixture of silt and Clay
   iii clay stone: Clay
   iv shale. Fissile (break along parallel planes)

Question 10

What are biochemical sedimentary rocks?

Answer 10

Produced by the chemical activity of organisms

Substances derived from solution by inorganic or biochemical processes

Question 11

What are the two textures of sedimentary rocks?

Answer 11

Crystalline- composed of mosaic of interlocking crystals

Classic- made up of fragments (sea shells flies together)

Question 12

What are the carbonate rocks?

Answer 12

Limestone- don’t need to scratch to react

Coquina limestone- fragmented seashells

Oolitic limestone- composed of ooids

Dolostone- forms when mg replaces some ca in limestone (scratch to react)

Question 13

What are the evaporates?

Answer 13

Halite

Gypsum

Chert- flint - dark chert
Jasper- red chert

Bitchomous coal

Question 14

What if peat?

Answer 14

Partially decayed plant remains found in low-oxygen waters

Converts from lignite - bitumous coal - anthrocite (99% carbon)

Question 15

What is sedimentary facies?

Answer 15

Bodies of sediment each possessing distinctive physical, chemical and biological attributes

Question 16

What are examples of sedimentary facies?

Answer 16

Marine transgression- sea level rises; shoreline moves inland

Marine regression- sea level falls; shoreline moves seaward

Question 17

Name and explain the 3 kinds of sedimentary structures (bedding)

Answer 17

Strata beds- layers of rocks

Cross bedding- angles angles with respect to depositional surface (ripple currents)

Graded bedding- upward decrease in grain size (turbidity current)

(Look at figures you made)

Question 18

Name and explains 5 more sedimentary structures

Answer 18

Ripple marks- small scale alternating ridges and troughs

Current ripple marks- streams leave behind asymmetric ripple marks

Waves- shallow marine ripple marks have a symmetrical shape from the rocking motion of the waves

Mud cracks- subjected to periodic drying

Fossils

Question 19

How to determine the environment of deposition?

Answer 19

Consider texture and other sedimentary structures

Use your understanding of natural processes, the principle of uniformitarianism (fossils in the Rockies)

ex. Navajo sandstone firmed as ancient sand dunes

Question 20

How are petroleum and natural gas form? (Hydrocarbon)

Answer 20

Micro organisms die in low oxygen bottom of seas of large lakes

The lack of oxygen prevent totally decay

Organic sediments are buried (temp must be just right)

Low density oil and/or natural gas migrates upward from the source rock

May reach the surface or accumulate in reservoir rocks underneath traps

Stratigraphic traps form cause of facies changed in rock layer

Structural traps form as the result of folding of fracturing (faulting) of rocks

Question 21

What is banded iron formation?

Answer 21

Alternating thin layers of chert and iron minerals, mostly iron oxides (hemitite, megnitite)

Nearly all of earths iron ore is mined from them